Increasing evidence suggests that high levels of reactive oxygen species (ROS) such as superoxide anion (O2 - ) and hydrogen peroxide (H2O2) play a pivotal role in the neurodegenerative process associated with Alzheimer's disease (AD) and Parkinson's disease (PD). In addition to their function as toxic molecules, ROS are recognized as effectors of redox-sensitive signaling pathways through enzymes such as the flavoprotein NADPH oxidase. Thus, excessive ROS may signal aberrant gene expression, leading to neuronal cell degeneration. However, the mechanism regulating free-radical induced neurodegeneration is unknown. NADPH oxidase has been shown to exist in neuronal cells and induce oxidative stress but its potential role as a mediator of prodeath signaling pathways has not been explored. Using a mouse and human neuronal cell model of neurodegeneration developed in our lab, we propose to characterize a putative NADPH oxidase-like complex that generates high ROS levels in response to cadmium, a potent inducer of oxidative stress. ROS production results in activation of the p38 mitogen activated protein kinase that, in turn, signals caspase-dependent apoptosis and neuronal cell death by a caspase-independent mechanism. This event is accompanied by induction of a neuroprotective pathway regulated by the vascular endothelial growth factor (VEGF). Cell death is attenuated by inhibition of p38, suggesting that ROS is an important regulator of stress-induced signaling pathways in neuronal cells. The intent of this proposal is to test the following hypotheses 1) use biochemical and genetic methods to determine whether an NADPH oxidase-like complex regulates ROS production and p38 activation in response to cadmium, 2) use biochemical and enzymatic methods to identify molecular events that distinguish p38-mediated caspase dependent apoptosis and caspase-independent neuronal cell death in response to cadmium and 3) determine the functional relationship between the activation of the prodeath pathway mediated by p38 and a VEGF-regulated prosurvival pathway induced by oxidative stress. It is our expectation that the resultant approach will identify the constituents of redox-activated signaling pathways that are induced in neuronal cells by oxidative stress to mediate prosurvival and prodeath functions. These results will be significant because they are expected to provide therapeutic strategies to alleviate the oxidative damage associated with AD or PD.